Balloons mounted on the distal ends of catheters are widely used in medical treatment.
When medical device balloons are made by radial expansion of a tubular parison, there is typically a significant difference in the amount of orientation between the inner and outer layers of the balloon because the radial expansion of material on the outer side of the parison is typically significantly less than that of material at the inner side of the parison.
Multilayer balloons made from coextruded layers of different polymers are described in various patents including U.S. Pat. No. 5,270,086 (Hamlin); U.S. Pat. No. 5,195,969 (J. Wang, et al.); U.S. Pat. No. 5,290,306 (Trotta, et al); U.S. Pat. No. 5,879,369 (Ishida); and U.S. Pat. No. 5,797,877 (Hamilton et al).
As an alternative to a coextruded parison balloon, U.S. Pat. No. 6,004,289 (Saab) describes medical balloons made by a successive process of extruding a parison, blowing a very thin wall balloon of inelastic material such as high molecular weight PET, trimming away a portion of the balloon cone and the waist, replacing the trimmed balloon portion in the mold, placing a second full length parison in the mold, blowing a second thin-walled balloon of the same material inside the portion of the first balloon within the mold to produce a second balloon that has two layers in at least the body portion and a portion of the cone. Optionally the second balloon may be trimmed to remove at least its waist and a portion of the cone not covered by the first balloon portion and the remnant replaced in the mold. Following placement of a third parison of the same material in the mold and blowing the third parison into the remnant of the second balloon, a third thin-walled balloon that has staggered layers in the cone region, and three layers in the body region is produced. This iterative process produces a balloon in which each layer is separately biaxially oriented with a relatively smaller difference between the expansion of the inner and outer sides of the parison so that very high orientation prevails throughout the balloon body. However the procedure is extremely tedious and labor intensive.
A less labor intensive tube-in-tube balloon process for forming multi-layer balloons is described in U.S. Pat. No. 5,587,125 (Roychowdhury). Polymer tubes of different, closely fitting, sizes are prepared, one in slipped over and drawn down on the other to produce a tube-in-tube parison, and then the balloon is blown from that parison.
In U.S. Pat. No. 6,124,007 (L. Wang et al.), a tube-in-tube parison is prepared after at least one of the two polymer tubes has been longitudinally oriented by axial stretching. The layers may be the same or different. Radial expansion of the tube-in-tube parison gives a balloon in which there is separate orientation of the two layers so that substantial additional strength is provided to the laminate balloon. However, in some cases the balloon layers are poorly bonded and delamination of the balloon may occur at burst. This is undesirable.